In vitro rearing of solitary bees: A tool for assessing larval risk factors

Authors: DHARAMPAL, PRARTHANA - University Of Wisconsin; CARLSON, CAITLIN - University Of Wisconsin; Steffan, Shawn

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2018
Publication Date: 7/16/2018
Citation: Dharampal, P., Carlson, C., Steffan, S.A. 2018. In vitro rearing of solitary bees: A tool for assessing larval risk factors. Journal of Visualized Experiments. 137(e57876). https://doi.org/10.3791/57876.
DOI: https://doi.org/10.3791/57876

Interpretive Summary: Conservation of crop pollinators is particularly important in fruit crop systems. Fungicide sprays on flowering plants may expose solitary bees to high concentrations of pollen-borne fungicide residues. Using laboratory-based experiments involving in vitro-reared bee larvae, this study investigates the interactive effects of consuming fungicide-treated pollen derived from host and non-host plants. This paper describes novel methods of in vitro culturing of solitary bee larvae, with/without maternal pollen and with/without fungicide residue. In the process, we reveal the potentially negative effects of non-maternal pollen-provisions and fungicide residues on larval bee survival. Because fungicide use is pervasive, these findings will inform new research into bee conservation strategies. US fruit crop growers will benefit from a better understanding of how best to conserve native pollinators.

Technical Abstract: Although solitary bees provide crucial pollination services for wild and managed crops, this species-rich group has been largely overlooked in pesticide regulation studies. The risk of exposure to fungicide residues is likely to be especially high if the spray occurs on, or near host plants while the bees are collecting pollen to provision their nests. For species of Osmia that consume pollen from a select group of plants (oligolecty), the inability to use pollen from non-host plants can increase their risk factor for fungicide-related toxicity. This manuscript describes protocols used to successfully rear oligolectic mason bees, Osmia ribifloris sensu lato, from egg to prepupal stage within cell culture plates under standardized laboratory conditions. The in vitro-reared bees are subsequently used to investigate the effects of fungicide exposure and pollen source on bee fitness. Based on a 2 × 2 fully crossed factorial design, the experiment examines the main and interactive effects of fungicide exposure and pollen source on larval fitness, quantified by prepupal biomass, larval developmental time, and survivorship. A major advantage of this technique is that using in vitro-reared bees reduces natural background variability, and allows the simultaneous manipulation of multiple experimental parameters. The described protocol presents a versatile tool for hypotheses testing involving the suite of factors affecting bee health. For conservation efforts to be met with significant, lasting success, such insights into the complex interplay of physiological and environmental factors driving bee declines will prove to be critical.